In any given geographical region, some portions of wireless spectrum may be licensed for exclusive use by particular wireless service providers/operators according to particular radio access technologies (RATs). Other, unlicensed portions of wireless spectrum may be concurrently used by multiple service providers/operators, and/or may be concurrently used for wireless communications according to multiple RATs. In order to accommodate the ever-growing demand for wireless broadband data services, it may desirable to use such unlicensed spectrum for 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)-based wireless communications. The use of unlicensed spectrum for LTE-based wireless communications may be referred to as LTE in Unlicensed Spectrum (LTE-U). In some systems, LTE-U may be combined with LTE-based wireless communications over licensed spectrum using carrier aggregation, a technique that may be referred to as Licensed-Assisted Access (LAA) using LTE, or simply LAA. In an LAA system, wireless communications in a primary cell (PCell) may be performed using an LTE licensed carrier, while wireless communications in one or more secondary cells (SCells) may be performed using one or more LTE-U carriers.
With respect to an unlicensed carrier, in order to support coexistence between a given LTE-U service provider/operator and other LTE-U service providers/operators and/or wireless communications performed according to other RATs, it may be desirable to implement a listen-before-talk (LBT) scheme. According to an LBT scheme, before initiating transmission over a given unlicensed carrier, a transmitting device may generally be required to substantially confirm that the unlicensed carrier is not already in use. In the context of an LTE-U carrier, an LBT scheme may require a transmitting evolved node B (eNB) or user equipment (UE) to perform a carrier sensing procedure, such as a clear channel assessment (CCA), before transmitting over the LTE-U carrier. According to some LBT schemes, the transmitting eNB or UE may be required to perform a backoff following a detection that the LTE-U carrier is already in use. In some geographical regions, it may be necessary to implement an LBT scheme in conjunction with communications over LTE-U carriers in order to comply with applicable regulations requiring the use of LBT when communicating over unlicensed spectrum. In other regions, LBT may not be required, but may still be a valuable technique for supporting fair coexistence between different service providers/operators and/or RATs with respect to unlicensed carriers.